Many advanced missiles utilize a generally forward-facing optical sensor to guide the missile to its target. The sensor (or, equivalently for the present purposes, a portion of the optical train that directs the incoming optical rays along an optical path from the scene to the sensor) is usually pivotably mounted so that the sensor may be directed to point in directions other than along the boresight axis (i.e., the axis of symmetry of the fuselage) of the missile. The sensor views the scene in front of the missile through a forward-facing dome window. The dome window protects the sensor from the high-velocity air stream and from impacts by water droplets, ice, dust, and other particles that are present in the air.
In some designs, the optical path of the sensor is coincident with a cylindrical axis of symmetry of the dome window when the optical train is pointed along the boresight axis of the missile. However, in other cases, the optical path of the forward-sensing sensor is laterally displaced from the axis of symmetry of the dome window when the optical path is pointed parallel to the boresight axis of the missile. The optical path passes through the dome window at a non-perpendicular angle that introduces aberrations into the image on the optical path. Such situations arise, for example, for a nose-mounted dome window when there are two or more sensors viewing the scene through the same dome window, so that at least one of the sensors must be laterally displaced from the axis of symmetry. They also arise when the sensor is a side-mounted but forward-sensing sensor rather than a nose-mounted forward-sensing sensor.
A decentered optical corrector segment may be positioned between the dome window and the optical train of the sensor to reduce the aberration. The decentered optical corrector segment has a spatially dependent shape that is selected responsive to the shape of the dome window to negate the aberration of the optical rays caused by the passage of the optical path through the dome window. The decentered optical corrector thus functions somewhat in the manner of eyeglasses worn by a human being. This approach, while operable, has drawbacks. Specifically, the fabrication, testing, mounting, and alignment of the decentered optical corrector segment are difficult, and the piece count of the system is high.
There is a need for an improved approach to optical systems wherein the optical path is laterally displaced from the boresight. The present invention fulfills this need, and further provides related advantages.